Impact of irrigation regime and nitrogen rate on yield, quality and water use efficiency of wild rocket under greenhouse conditions

In Italy, the cultivation of wild rocket is still rising due to the increase of the market of minimally processed vegetables that requires innovative and high quality products. The present study focused on the interactive effect of irrigation regimes (IR) and nitrogen (N) supply on yield, water use efficiency (WUE), nitrogen use efficiency (NUE), morphological and quality parameters of wild rocket. The research was carried out on four crop cycles during autumn-spring season in Basilicata region, Southern Italy, on wild rocket grown in a plastic greenhouse. Four IR (corresponding to 75, 100, 125 and 150% of crop evapotranspiration, and labelled respectively as I75, I100, I125 and I150) and two N levels (60 and 120 kg ha-1), were compared. The irrigation and N levels affected production traits of wild rocket. The highest yield was obtained by I100, while 8% and 6% decrease in yield was observed with I75 and I150, respectively. The greater yield was obtained with the higher N rate, to which contributed firstly the leaf number and secondly the leaf size. However, the higher N dose provided higher leaf nitrate content. Moreover, in conditions of greater water stress occurring in the last two crop cycles of I75, higher N rate adversely affected yield. Lower water and N supply improved phenols, carotenoids and antioxidant activity in rocket leaves. Both yield and biomass WUE increased in water shortage conditions (I75) at 1st crop cycle. Thereafter, both parameters tended to decrease because of the increase of water shortage, indicating that biomass and marketable yield losses were proportionally greater than the amount of water used by crops. Higher N rate improved WUE, but reduced NUE. The latter parameter was higher in water shortage conditions. Thus, adequate water and N supply are critical factors to ensure economically sustainable production levels and high quality features of wild rocket.